This invention relates to a telephone set, and more particularly is directed to an improved telephone set having a loud speaker and a conventional handset.
A conventional telephone set usually includes a ringing circuit, a telephone circuit, a handset and a hook switch. When the telephone set is in an idle state, i.e., waiting to be used, the ring circuit is connected to a pair of telephone lines by the hook switch so that a ring signal from the telephone exchange or local central office can be detected. When the ring signal is detected, a bell or other alarm or indicator is activated to signal an incoming call. When the telephone user responds to an incoming call or wishes to make a call and picks up the handset, the hook switch disconnects the telephone lines from the ringer circuit and connects them to the telephone circuit. The user may then complete the telephone call. In this embodiment of a conventional telephone apparatus, the hook switch is automatically operated by the operation of the handset.
In recent years, telephone sets have been developed which have a loud-speaker and associated circuitry in addition to the conventional circuitry mentioned above. Thus the telephone user can hear the conversation without using the telepone handset. Other telephone sets have been developed which have a speaker/microphone. A speaker/microphone permits the telephone user to freedom to move about a room while still carrying on a telephone conversation. It also allows several persons to be involved in the conversation at the same time.
One embodiment of a conventional telephone set is shown in block diagram form in FIG. 1. In FIG. 1, telephone lines 1 and 2 are normally connnected to ringing circuit 3 through first hook switch 14, relay contact 27T of relay 27, capacitor 6 and diode bridge circuit 5. Ringing circuit 3 detects the presence of a signal from the telephone exchange or local central office. The signal is converted to a ring tone or other indicator by sounder 4. When the telephone user picks up handset 10 to respond to an incoming call or wishes to place a call, first hook switch 14 and second hook switch 15 are activated. Hook switches 14 and 15 are always activated together inr esponse to taking handeset 10 off its hook. The automatic operation of hook swithces 14 and 15 is performed by a linkage (not shown) as is well known int he art. The operation of first hook switch 14 causes telephone lines 1 and 2 to be disconnected from ringing circuit 3 and to be connected to telephone circuit 9 through first hook switch 14, diode bridge circuit 17 and dialing circuit 13. Control circuit 18 generates a control signal which enables telephone circuit 9 when second hook switch 15 is activated. Consequently, the user can talk into telephone lines 1 and 2 through handset 10. The user may also dial a desired telephonenumber using dial keys 19. Control circuit 18 provides a control signal which causes dialing circuit 14 to generate respective dial tones which are sent to the telephone exchange when dial key 19D are activated by the user.
The telephone set further includes speaker 12 and receiving circuit 11. Speaker 12 permits the telephone user to hear the telephone conversation without the aid of handset 10. Thus, the telephone set may be used in a hands-free mode. When the telephone user desires to use speaker 12, the hands-free mode is selected by, e.g., operating one of dial keys 19, i.e., dial key 19HF. In response to the operation of dial key 19HF, circuit 18 generates a control signal which causes relay 27 to operate. Relay 27 includes relay contacts 27T which are operated to move from first contact point 27CI to second contact point 27C2 and to cause receiving circuit 11 to operate. Telephone lines 1 and 2 are thus connected to receiving circuit 11 through switch 14, relay contact 27T, second contact point 27C2, diode bridge circuit 17 and dialing circuit 13. The user then hears the activity taking place within the telephone system on speaker 12. Thus, when a party being called answers the phone, the user may pick up the handset 10 to begin the conversation. When handset 10 is removed from it shook, the connection of telephone lines 1 and 2 is changed from receiving circuit 11 to telephone circuit 9 in accordance with control signals from controlling circuit 18 as described above. Thus, the user may engage in an ordinary telephone conversation using handset 10.
In the above embodiment of a conventional telephone set, the receiving circuit is used for hands-free receiving. However, any other hands-free circuit may be used as well.
In the telephone set described above, a relay is used to switch the connection of telephone lines 1 and 2 between receiving circuit 11 and telephone circuit 9. A relay, however, takes a relatively large amount of space and is high in cost. Moreover, a relay has a rather short life span and can not be depended on for extended reliable operation. Thus, there is a need in the art for a more reliable telephone set.